Primordial black holes as a natural consequence of scale-invariance
A scale-invariant U(1) gauge theory naturally produces large curvature perturbations during thermal inflation around its end. A specific nonminimal gravitational interaction ($\xi \sim O(1)$) causes a phase transition that ends inflation while keeping extra e-folds small. This mechanism amplifies thermal fluctuations to seed primordial black holes (PBHs), leading to observable correlated gravitational wave signatures.